The CPUfreq plugin shows always the clock frequency of the last CPU, regardless of which CPU has been selected in the options. The problem is that the function cpufreq_update_plugin in xfce4-cpufreq-configure updates the label and tooltip for all cores, so that the text is always overwritten with the information about the last core:

	gint i;
	for (i = 0; i < cpuFreq->cpus->len; i++)
	{
		CpuInfo *cpu = g_ptr_array_index (cpuFreq->cpus, i);
		if (cpufreq_update_label (cpu)   == FALSE)
			return FALSE;
		if (cpufreq_update_tooltip (cpu) == FALSE)
			return FALSE;
	}

I suggest something like:

        gint i = cpuFreq->options->show_cpu;
        CpuInfo *cpu = g_ptr_array_index (cpuFreq->cpus, i);
        if (cpufreq_update_label (cpu)   == FALSE)
          return FALSE;
        if (cpufreq_update_tooltip (cpu) == FALSE)
          return FALSE;